1. Field of the Invention
The present invention relates to an engine in which a sprocket is fixed to one end of a camshaft and a timing chain is wrapped around the sprocket and, in particular, to a timing chain lubricating system therefor.
2. Description of the Related Art
A camshaft of an overhead camshaft type engine is driven by an arrangement in which a sprocket fixed to a shaft end of the camshaft is linked to a sprocket fixed to a shaft end of a crankshaft via a timing chain. A lubricating system for such a timing chain is known in Japanese Patent Application Laid-open No, 6-146838. The timing chain lubricating system disclosed in the above-mentioned application has an arrangement in which a relief valve is provided in an oil passage for supplying oil to a hydraulic tappet, and the section where the sprocket is meshed with the chain is lubricated with a jet of oil that issues from an oil jet that is integral with the relief valve,
In the above-mentioned conventional arrangement, since the oil jet can lubricate only one position of the timing chain, when the amount of oil required and the position that is to be lubricated change according to the operational state of the engine, it is difficult to carry out appropriate lubrication according to the changes.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to enable a timing chain wrapped around a sprocket of a camshaft to be reliably lubricated according to the operational state of an engine.
In order to achieve the above-mentioned object, in accordance with a first aspect of the present invention, there is proposed a timing chain lubricating system for an engine in which a sprocket is fixed to an end of a camshaft and a timing chain is wrapped around the sprocket, comprising a plurality of oil supply means for supplying oil to the timing chains the operation of the plurality of oil supply means being changed according to the operational state of the engine.
In accordance with the above-mentioned arrangement since the operation of the plurality of oil supply means for supplying oil to the timing chain is changed according to the operational state of the engine, lubrication can be carried out according to the operational state of the engine thus reducing the wear of the timing chain.
Furthermore, in accordance with a second aspect of the present invention, in addition to the above-mentioned first aspect, there is proposed a timing chain lubricating system for an engine, wherein the number of oil supply means that are in operation is increased as the rotational speed of the engine or the engine load increases.
In accordance with the above-mentioned arrangement, since the number of oil supply means that are in operation is increased as the rotational speed of the engine or the engine load increases, the number of positions that are lubricated can be increased according to the rotational speed of the engine or the engine load thus further effectively reducing the wear of the timing chain,
Furthermore, in accordance with a third aspect or a sixth aspect of the present invention, in addition to the above-mentioned first aspect or second aspect, there is proposed a timing chain lubricating system for an engine, further comprising variable valve lift means for changing the relationship between the size of the valve lift of an intake valve and the size of the valve lift of an exhaust valve according to the operational state of the engine, the amount of oil that is supplied to the section where the sprocket that drives the valve having a large valve left is meshed with the timing chain being made larger than the amount of oil that is supplied to the section where the sprocket that drives the valve having a small valve lift is meshed with the timing chain.
In accordance with the above-mentioned arrangement, since the relationship between the size of the valve lift of the intake valve and the size of the valve lift of the exhaust valve is changed by the variable valve lift means so that the amount of oil that is supplied to the section where the sprocket that drives the valve having a large valve lift is meshed with the timing chain is larger than the amount of oil that is supplied to the section where the sprocket that drives the valve having a small valve lift is meshed with the timing chain, a larger amount of oil can be supplied to the sprocket having a larger valve operating load so prolonging the life span of the timing chain.
Furthermore, in accordance with a fourth aspect, a fifth aspect or a seventh aspect of the present invention, in addition to any one of the above-mentioned first aspect to third aspect, there is proposed a timing chain lubricating system for an engine, further comprising a hydraulic control valve for switching over between a low speed valve lift and a high speed valve lift, the low speed valve lift being used when the rotational speed of the engine or the engine load is lower than a predetermined value, the high speed valve lift being used when the rotational speed of the engine or the engine load is higher than a predetermined value, the timing chain being lubricated with relief oil from the hydraulic control valve when the low speed valve lift is established and the timing chain being lubricated with valve lift control oil from the hydraulic control valve when the high speed valve lift is established.
In accordance with the above-mentioned arrangement in which the hydraulic control valve establishes a low speed valve lift when the rotational speed of the engine or the engine load is low and a high speed valve lift when the rotational speed of the engine or the engine load is high, when the low speed valve lift, which imposes a low load on the timing chain, is established the timing chain is lubricated with relief oil from the hydraulic control valve; when the high speed valve lift, which imposes a high load on the timing chain, is established the timing chain is lubricated with valve lift control oil from the hydraulic control valve, aid an amount of oil that is appropriate for the state of the load can thus be supplied to the timing chain so effectively preventing wear of the timing chain.
Furthermore, in accordance with an eighth aspect of the present invention, in addition to the above-mentioned first aspect there is proposed a timing chain lubricating system for an engine, further comprising an oil jet that issues a jet of chain lubricating oil when the rotational speed of the engine or the engine load is higher than a predetermined value.
In accordance with the above-mentioned arrangement, since the oil jet issues a jet of chain lubricating oil when the rotational speed of the engine or the, engine load is higher than the predetermined value, it becomes easy to supply oil to the timing chain.
Furthermore, in accordance with a ninth aspect of the present invention, in addition to the above-mentioned first aspect, there is proposed a timing chain lubricating system for an engine, further comprising an oil jet and a hydraulic control valve for switching over between a low speed valve lift and a high speed valve lift, the low speed valve lift being used when the rotational speed of the engine or the engine load is lower than a predetermined value, the high speed valve lift being used when the rotational speed of the engine or the engine load is higher than the predetermined value, the timing chain being lubricated with relief oil from the hydraulic control valve when the low speed valve lift is established and the timing chain being lubricated with valve lift control oil from the; hydraulic control valve via the oil jet when the high speed valve lift is established.
In accordance with the above-mentioned arrangement in which the hydraulic control valve establishes a low speed valve lift when the rotational speed of the engine or the engine load is low and a high speed valve lift when the rotational speed of the engine or the engine load is high, when the low speed valve lift, which imposes a low load on the timing chain, is established the timing chain is lubricated with relief oil from the hydraulic control valve; in the high speed valve lift, which imposes a high load on the timing chain, is established the timing chain is lubricated with valve lift control oil from the hydraulic control valve via the oil jet, an amount of oil that is appropriate for the state of the load can thus be supplied to the timing chain so effectively preventing wear of the timing chain and, moreover, it becomes easy to supply oil to the timing chain.
Furthermore, in accordance with a tenth aspect of the present invention, in addition to the above-mentioned eighth aspect, there is proposed a timing chain lubricating system for an engines wherein the camshaft is supported by an upper camshaft holder and a lower camshaft holder and the oil jet is fastened to the lower camshaft holder.
In accordance with the above-mentioned arrangement, since the camshaft is supported by the upper camshaft holder and the lower camshaft holder and the oil jet is fastened to the lower camshaft holder, the rigidity with which the camshaft and the oil jet are supported can be enhanced,
Furthermore, in accordance with an eleventh aspect of the present invention, in addition to the above-mentioned eighth aspect, there is proposed a timing chain lubricating system for an engine, further comprising a relief oil discharge hole, the relief oil discharge hole and the oil jet being disposed on the side of the sprocket that is close to the hydraulic control valve.
In accordance with the above-mentioned arrangement, since the relief oil discharge hole and the oil jet are disposed on the side of the sprocket that is close to the hydraulic control valve, the oil passage can be shortened,
Furthermore, in accordance with a twelfth aspect of the present inventions in addition to the above-mentioned eleventh aspect, there is proposed a timing chain lubricating system for an engine, wherein the oil jet lubricates the section where the sprocket is meshed with the chain on the side that is far from the hydraulic control valve
In accordance with the above-mentioned arrangement, since the oil jet lubricates the section where the sprocket is meshed with the chain on the side that is far from the hydraulic control valve, it becomes easy to supply oil to the section to be lubricated.
An intake camshaft 12 and an exhaust camshaft 13 of the embodiments correspond to the camshafts of the present invention, an intake camshaft sprocket 15 an exhaust camshaft sprocket 16 of the embodiments correspond to the sprockets of the present invention, an oil drain hole 25b and an oil jet 36 of the embodiments correspond to the oil supply means of the present invention, a first hydraulic control valve 34 of the embodiments corresponds to the hydraulic control valve of the present invention, and a fist variable valve operating characteristic mechanism V1 of the embodiments corresponds to the variable lift means of the present invention.
Furthermore, the above-mentioned predetermined value for the engine rotational speed is, for example, 2500 rpm when the valve lift is switched over on the low speed side and, for example, 5000 rpm when the valve lift is switched over on the high speed side, but it is not limited thereby,